It's refreshing to see a senior in high school who doesn't know everything. Unfortunately we weren't born with innate knowledge of everything we need to know in life.
You are not stupid! The trike you mention is affordable and readily available but unless your boyfriend is willing to ride extremely slowly, it will not work as a trike to ride along with him. It has only one speed and the weight is 70 pounds. That works great for someone in a retirement community who wants to ride around the complex but doesn't intend to ride it any significant distance. These adult trikes also come in 3-speed models but still weight a lot more than I would ever be willing to pedal.
You can read the specifications here: https://alladulttricycle.com/26-schw..._Specification. Price is a tad over $300. The one answer in Q&A that caught my eye:
Q:Will I be able to carry it upstairs? The trike weighs in at 70 pounds, which is quite heavy, and it would need the combined effort of about 2 people to carry it. Given its width, it might not be able to go up a flight of stairs in the case of narrow stairways. That goes the same for lifting it off the ground too.
A recumbent trike would serve your needs much better but I am afraid that the price would be way outside of what a high school senior could afford. Even the cheapest ones are over $1K and used trikes rarely go for less than half of that.